docs: def make_market(self, crypto, fiat, seperator="_"):
          """
          Convert a crypto and fiat to a "market" string. All exchanges use their
          own format for specifying markets. Subclasses can define their own
          implementation.
          """
          return ("%s%s%s" % (
              self.fix_symbol(crypto), seperator, self.fix_symbol(fiat))
          ).lower()